Catalysts for the production of ethylene oxide from ethylene and molecular oxygen generally comprise silver supported on a carrier formed substantially of alpha alumina. Such catalysts are typically promoted with alkali metals. Other co-promoters, such as rhenium, or rhenium along with sulfur, molybdenum, tungsten and chromium can also be utilized. See, for example, U.S. Pat. No. 4,766,105, issued Aug. 23, 1988. While much research has been focused on promoters, more recently, work has been focused on the alumina supports and ways to modify them to produce improved catalysts.
European Patent Application 247,414, published Dec. 2, 1987, discloses the addition of silica to an alpha alumina carrier. U.S. Pat. No. 4,428,863, issued Jan. 31, 1984, discloses the addition of barium aluminate or barium silicate to alumina carriers during their manufacture. In U.S. Pat. No. 4,728,634, issued Mar. 1, 1988, silicon dioxide and an alkali metal salt are mixed with water and an aluminum compound and calcined to produce a silica- and alkali metal-containing alpha alumina support. In U.S. Pat. No. 4,874,739, Oct. 17, 1989, a tin compound and an alkali metal compound is incorporated into an alpha alumina carrier.